Oceanographic research uses sensing devices for the determination of parameters including but not limited to temperature, salinity, and the presence of solutes. Such devices to record or transmit data underwater will require housings. The sensing devices are housed within a container adapted to withstand the oceanic hydrostatic pressure that increases as depth increases. Deep ocean research therefore demands housings for instrumentation or sensors that can withstand pressures found at depths up to 36,000 feet of water.
Providing pressure protection for electrical, electronic, and mechanical components in a high-pressure fluid environment is in many cases essential to maintaining proper performance of these components. Undersea instrumentation packages and other submersibles are subjected to pressure in direct relation to the depth at which they are being used.
In underwater sensing systems, the instruments and the other fixtures contained in the pressure housings often require that specific structural considerations be examined. These structural considerations, in many instances, require that it is necessary to minimize overall system size or weight in order to simplify system handling, launch, or recovery operations as well as to reduce cost.
Some underwater systems require that the overall system be neutrally buoyant, and in some cases slightly negative, or even positive. This buoyancy is typically achieved in one of two ways: 1) by either supplying buoyant material, or 2) the empty volume by within the system. Therefore, minimizing the weight of a system also allows for a reduction in the buoyant material or in the structural volume required to achieve the overall desired state of system buoyancy. An example of such a system is an oceanographic instrument package which must be neutrally buoyant during its operation. Decreasing the weight of the pressure housings would allow the volume of the system, as a whole, to be reduced. The volume, of a cylinder for example, can be reduced by either reducing the diameter, the length, or both. This reduction results in less water that has to be displaced to achieve the overall buoyant force requirement. A reduced diameter may also result in other advantages, such as decreased system size, extended mission duration, or simplified handling. Also, the cost of underwater pressure housings increases dramatically as the size increases. This illustrates a principle advantage of the instant invention over the prior art. The use of ceramic cylinders in pressure housings allows for a reduction in weight and is well known in the prior art. See Design of a Deep-Ocean Pressure Case Using a Ceramic Tube, Ceramic Bulletin, Vol. 46, No. 12, C.R.B. Lister, 1967. However, the effective use of ceramic cylinders requires specific techniques that are within the embodiments of the instant invention.
Certain ceramic materials have been found to be desirable for the fabrication of pressure housings due to their impermeability, high-compressive strength, low cost, and ease of fabrication. In order to provide pressure protection, cylindrical pressure housings must be sealed by endcaps to complete the pressure boundary. Electrical or mechanical penetrations must often be made through these endcaps via electrical connectors or mechanical feedthroughs. There is a continuing need for pressure housings that assure reliable long-term operation at low cost.
The housings, now in use in the prior art, are typically built using Titanium (6AL-4V), Aluminum alloy (6061 or 7075) or stainless steel (303, 304, or 316) with O-ring seals. The disadvantage of the prior art is that those pressure housings have complex titanium rings bonded to the ceramic housing (using epoxy based adhesive) with a secondary O-ring seal incorporated to provide final sealing. Such housings have several important disadvantages. In addition to having a complicated double ring sealing system, those that use ceramic cylinders must be machined, which is very expensive.
The housings described herein do not require machining following the firing of the ceramic material. Machining of ceramics which have already been fired is a costly and time-consuming process.
The housing described herein also is low in cost when compared to the conventional machining methods that require very tight tolerances be maintained.